The proposed research is concerned with neuroendocrine regulation of reproductive behavior. There are three main project areas. 1) Regulation of the postejaculatory refractory period and postejaculatory vocalization. Studies on the neurological substrate of the postejaculatory refractory period and on the hormonal involvement in the development of postejaculatory behavior. 2) Neuroendocrine regulation of proceptive and receptive behavior of female rats. Experiments on the hormonal control of proceptive behavior and on sites of action of sex hormones in the brain in the regulation of proceptive and receptive behavior. 3) The role of ultrasonic vocalization in rat reproductive behavior. Recording and play back of ultrasonic vocalizations to assess the communicatory function of these sounds in rat mating behavior.